Electric control system



y 1948- B. D. BEDFORD 2,445,991

ELECTRIC CONTROL SYSTEM Original Filed June 12, 1944 2 Sheets-Sheet 1 Inventor I Burnice D. Bedfprd,

His Afitor'neu.

July 27', 1948. B. D. BEDFORD 2,445,991

ELECTRIC CONTROL SYSTEQA Original Filed June 12, 1944 2 Sheets-Sheat 2 His Abborneg Patented July 27, 1948 mcr'mc oomor. SYSTEM em 1). more, Scotia, N. Y., assignorto General Electric Company, a corporation of 7 New York Original application June 12, 1944, Serial No.

539,942. Divided and this 5, 1946, Serial No. 652,169

(Claims.

My invention relates to an electric control system and more particularly to an electric control system for dynamo-electric machines.

This application is a division of my application Serial No. 539,942, filed June 12, 1944, entitled "Electronic converter, now Patent No. 2,435,187 01' February 3, 1948, and assigned to the assignee of the present application.

In order to illustrate my invention, I will describe it as applied to a phase control system in an electronic converter system of the dual conversion type wherein alternating current is rectifled by an electronic converter to 'direct current and then reconverted by a second electronic converter from direct current to alternating current. 'Since electronic converter apparatus of the dual conversion type involves both rectification and inversion, accurate firing of each tube of the inverter is essential and in a reversible power flow type, as herein described, either group of tubes at the respective ends of the system may have to operate as an inverter. Hence, such a system requires a flexible, accurate and quickly responsive phase control system without undue complications. The particular phase control system illustrated utilizes a readily controllable and reversible direct current source of voltage and in accordance with my present invention, I provide a new and improved control system for a dynamo-electric machine which is particularly well adapted for use in the phase control system illustrated but which may have general application in various other applications as will be evident to those skilled in the art.

It is, therefore, an object of my invention to provide a new and improved electric control system for a dynamo-electric machine.

It is another object of my invention to provide a new and improved electric control system for a dynamo-electric machine utilized in an elec-' tronic power conversion system.

It is a further object of my invention to provide a new and improved electric control system for an amplidyne generator.

My invention will be better understood from the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the drawings, Figs, 1 and 2, taken together, are a diagrammatic representation of one embodiment of my invention as utilized in a complete dual conversion electronic system, whereas Fig. l or Fig, 2, considered separately, is a diagrammatic representation of an embodiment oi.

application March my invention as utilized in a single step electronic conversion system.

Referring to the drawings, and for the present to Figs. 1 and 2 considered together, I have shown an alternating current circuit l which is to be interconnected with an alternating current circuit 2. I will consider first the power circuits and to facilitate the description will refer, by way of example, to circuit l as a cycle powercircult.

and the tube groups associated therewith as rectifiers, and the circuit 2 as a 25 cycle power circuit and the tube groups associated therewith as inverters. It is to be understood, however, that the power circuits may be of any desired power frequency of the same or of diil'erent frequencies, and that the tube groups associated with either power circuit may be operated as rectifiers or inverters. Under the assumed conditions of function, I have illustrated in Fig. 1

two tube groups 3 and 4- 0! six tubes each, arranged for three phase full wave rectification, and with tubes which are degrees apart in phase position mounted back to back with the cathode oi one tube connected to the anode of another. In Fig. 2, I have illustrated two tube groups 5 and I of six tubes each. similarly arranged tor three phase full wave inversion. The tube groups 3, I, 5 and 6 are connected alternately in series in a direct current loop comprising conductors la, 3b, 40. and 4b which include direct current reactors 1' connected in series between each rectifier and inverter. The alternate arrangement of the 25 and 60 cycle tube groups in the direct current loop minimizes the voltage level and is a feature described and claimed in an application oi A. Schmidt, Serial No. 539,939, filed June 12, 1944, now Patent No. 2,419,464 or April 22, 1947, and assigned to the assignee of the present application.

The rectifiertube groups 3 and 4 are connected to the alternating current circuit I through transformers I and 8 which are designed and connected to obtain multi-phase operation. One arrangement which has been found to be satisfactory in service is to utilize two three-phase secondary windings 9 and Ill, displaced from each other thirty degrees, which may be obtained by connecting a primary winding ll associated with secondary winding 9 in delta connection and a primary winding I2 in Y connection associated with secondary winding Ill. The inverter type groups 5 and i are similarly connected to the alternating current circuit 2 through transformers l3 and I4 having, respectively, Y-connected secondary windings l5 and I6 and delta and Y- connected primary windings l1 and I8. Between each grou of transformer secondary windings actors I9 and are introduced to limit the fault currents during arc-backs or a short circuit on the direct current loop.

The three-phase double-way (full wave) circuit illustrated is particularly desirable because of its high apparatus economy and good operating characteristics. Although various types of tubes may be used, I have found in practice that of the presently available commercial forms a type known in the art as a pentode ignitron is satisfactory for large power commercial use. For the details of this type of tube, reference may be had to U. S. Letters Patent No. 2,209,819

granted July 30, 1940, upon an application of K. HIKingdon and assigned to the assignee of the present invention. For the purpose of explaining my invention as utilized in the converter system illustrated, it will suffice to refer to one of the pair of tubes of tube group 4 which is to be taken as representative of all of the other tubes. Each tube comprises an anode 2|, 8, mercury'pool type cathode 22, an immersion-ignitor member 23, a holding anode 24 and a control member or grid 25. The immersion-ignitor 23 establishes a cathode spot by conducting a current peak of short duration whereupon an arc is established and maintained by the holding anode Thegrid 25 is utilized to determine the time of starting conduction between anode and cathode and also reduces the cleionization period at the end of conduction.

Power for both the grid and ignition circuits of the assumed 60 cycle end is obtained from an auxiliary power transformer 21 which is utilized to energize an auxiliary power bus 21a. The transformer 21 may be connected to the power circuit l as illustrated, or to a supply source correlated in frequency and in phase with the power circuit 1. Thus, three phase power is delivered by the bus 21a to lines 28, 29 and 30, which in turn are connected through variable impedance devices such as saturable reactors 3|, I2; 23, l4 and 35, 36 to switching means R and I which may take the form of two six pole contactors wherein R signifies the rectifier contactor and I signifies the inverter contactor. These contactors introduce the grid phase shift necessary for reversing power flow which will be explained in detail later. Suitable interlocks (not shown) will, of course, be utilized to prevent simultaneous closing of the R and I contactors. These contactors connect the three-phase A.-C. lines 28, 29 and to the twelve phase network 28. This network compi'ises a plurality of inductive windings arranged diagrammatically inthe form of a and its associated tube group current limiting re- 1 polygon and for the illustrated embodiment of my invention comprises a twelve-sided polygon consisting of windings identified in a-counterclockwise order from the twelve o'clock position as windings 31 to 48, inclusive, The Junction points of the windings'starting with the twelve o'clock position are identified in a counterclockwise direction by the points 49 to 60, inclusive. Stabilizing windings 6| to 86 interconnect, respectively, the junction points is to 58, to 55, 51 to II, 54 to ll. 53 to 50 and 50 to 59. Each of the several groups of windings in parallel physical relation considered diagrammatically, such as the triplet of windings 48, 66 and 42, would be placed on'the same magnetic core (not shown). Each of the peripheral windings 31 to 48, inclusive, may be provided with taps for cor- '4 rection of the respective excitation circuits but to avoid undue'complexity in the drawings only those taps required for the excitation circuits illustrated will be referred to later.

The reactors 3! to 36 are direct current saturated reactors. In accordance with the illustrated embodiment of my invention one group of flux bias windings or presaturating windings 61 to 12 are connected in series relation each with the same polarity in additive relation and energized from any convenient, relatively constant, D.-C. source which, as illustrated, may be obtained from the bus 21a through a full wave rectiiier 13p. The windings 61 to 12 are associated with the A.-C. reactor windings 3| to 36 in the same order as the numerals have been specified and the current direction assumed is indicated by the arrows associated with windings 61 to 12. A group of control saturating windings 13 to I8 are connected in series relation but with the odd numbered windings of this series reversed in polarity relative to the even numbered windings. Due to the reversal of the odd numbered control reactors relative to the even, in combination with the presaturated windings, a variation in direct current through the control saturating windings affects the odd and even numbered reactors oppositely. Thus an increase in the control saturating current increases the saturation of, say, the odd numbered reactors by aiding the preseturating winding and decreases the saturation of the even numbered reactors by opposing the presaturating winding, whereas a decrease in saturating current causes the reverse eifect. Phase advance on the 12-phase polygon 26 is considered to be effected tin the conventional counterclock- 'wise direction when the odd numbered reactors are being saturated while the even numbered reactors are being unsaturated. It is thus possible to shift the grids through the available range of 90 degrees by reversing the current in the control saturating windings although in the particular arrangement utilized a shift-substantially degrees may be effected without current reversal. For each value of. saturating current there is a corresponding phase position of the network 26. Shifting the effective point of entry of the supply conductors 28, 29 and '30 to the 12-phase network by D.-C. saturation shifts the operating phas of the two 6-tube groups 3 and 4 without disturbing their 12-phase relation, and without disturbing the timing of the ignitors, grids and holding anodes for any tube. These control saturating windings 13 to 18 are connected to be variably energized from a controllable source of direct current such as a controllable dynamoelectric machine provided with an electric control system in accordance with my present invention.

It will be apparent from the foregoing description of the illustrated embodiment of my invention that for each pair of impedances or saturable reactors the same effect is produced if th bias or presaturating windings are arranged in opposed relation and the control windings in additive relation. The principal of control is dependentupon effecting an inverse change in the respective impedances of each pair of imped- 28, 29 and 30 will be connected through the D.-C.

saturated reactors to two points on the twelveand ",and line 99 is connected to points 92 and II through reactors 99 and 99. If the odd numbered reactors 9|, 99 and 99 are fully saturated and the even numbered reactors 92, 94 and 99 are unsaturated, lines 99,- 19 and 99 are closely connected to the points 99,99 and II. This condition is taken to represent a fully advanced position. Reversing the saturation of tlm'reactors. so that the odd numbered reactors are unsaturated and the even numbered reactors are fully saturated, in effect shifts the points of entry of lines 29, 29 and 99 ninety degrees .to

points II. II and II, respectively. This shift in that the 12-phase network 99 with the R con-v tactor closed can be given a 90-degree phase shift by reversing the saturation of the direct current reactors. When the I contactor is closed (all I switches closed) and the R switches opened, the saturating reactor spans an angle of only about 60 degrees and the grids may be advanced continuously through an angle ofv the order of 60 degrees beginning at a predetermined angle of advance of the grid voltage for inverter operation. This shift in phase for either rectifier or inverter is fairly continuous upon variations in the saturating current in accordance with the principles recited above. The voltage variation of the network 29 need not exceed 10% over a phase shift of 90 degrees, and it has been found that the time required for a complete phase shift of 90 degrees need not exceed 0.1 second for a 60 cycle network. All tube control power for the grids, ignitors and holding anodes for the 60 cycle tube groups 9 and l is furnished by the single network 29.

In accordance with my present invention, the variable direct current energization for the control saturating windings of the phase-shift network 29 is obtained from a. readily controllable and reversible direct current source of voltage,

which is illustrated as a direct current dynamoelectric machine I9. Although various known types of direct current dynamo-electric machines may be utilized to carry out my invention in its general aspects, I have found in practice that a. particularly suitable type is the compensated cross-armature reaction excited machine known in the art as an amplidyne generator such as is described and claimed in United States Letters Patent No. 2,227,992, granted January 7, 1941, upon an application of E. F. W. Alexanderson and M. A. Edwards and assigned to the assignee of the present application. The machine I9 is, therefore, illustrated with a pair of short circuit brushes II for providing the main armature reaction excitation of the machine and a pair of load brushes 99 which are displaced from the short circuit brushes 99. The machine is also provided with a number of control field windings which may be identified by their respective functions as the anti-hunt winding 99, cu'rrent limit field 94, load transfer field 99 and main Points 99 and 9| are control field 99. To facilitate an explanation of the operation .of the system, it will be assumed that a positive field terminal to the right, that is,

withcurrent fiow from right to left (Fig. 1) results in a positive terminal of the left-hand brush 92 of generator I9. This convention is just the opposite in ,Fig. 2 since that drawing, in

so far as the corresponding dynamo-electric machine is concerned, is in effect a mirror image of Fig. 1. The-left-hand load circuit brush 92 is connected directly to the terminal winding 19 of the series of saturable reactor control windings II to 19. The right-hand-load circuit brush "is connected through an inductive coupling device 99 and a resistor 99 to the terminal winding of the winding 19 of the saturable reactor control windings.

The anti-hunt circuit of field winding 99 will now be considered. The inductive coupling device '99 is provided with a secondary winding 9| having two end terminals and an intermediate terminal 92. One end terminal of winding 9| is connected directly toone terminal of the antihunt winding 99. and the other end terminal is connected through an R switch 99 to the midpoint of twoseries connected resistors 94 and 99. These resistors, in turn, have a circuit in shunt thereto and including a contact rectifier poled to pass current in the direction indicated by the arrow. In a similar manner, the intermediate taps: is connected through an I switch 91 to the midpoint of two resistors 99 and 99. These resistors, in turn, are provided. with a shunt circuit including a. contact rectifier l'llli poled in a direction to pass current in the direction indicated by the arrow. The R and I switches here,

as well as in all other cases in the drawing, are

interlocked so that when the R switches are closed the I switches are open and vice versa. The antihunt circuit may be better understood by considering the R switch 93 closed and the I switch 91 open. In this case it will be observed that the circuit of field winding 99 may be traced from the right-hand terminal of the winding 9|, considered as a source of positive voltage if the current increases for the polarity of the generator indicated, through the R switch 99 with one path through resistor and another .parallel branch path through resistor 94 and rectifier 99, to the left-hand terminal of winding 99 with current through the winding from left to right. Thus the winding 9| picks up a, transient voltage as the armature current increases. This voltage is in a direction to energize the anti-hunt field 93 in a direction to make the left-hand brush less positive and thus oppose the change in armature current. If the change is in one direction the current has the two paths traced above and due to the relatively low impedance as contrasted with the one path the anti-hunt effect is the greatest. However, if the change of current is in the opposite direction or a decrease only the single path through resistor 95 is available and due to the relatively'higher impedance the anti-hunt efiect is less. The arrangement, therefore, provides ad- Justments for obtaining different anti-hunting eifects, depending upon the direction of change. The same operation is effected with the I switch 91 closed and the R switch 93 opened through the resistors 99. and 99 and the rectifier I09. In this case only a portion of the winding 9| of the inductive device need be used;

The energization and controlof the current limit field 94 may now be considered. One important feature of the control limit field 94 is its armature current beyond the value of control current or ampere turns at which the control current effect was greater than the'bias or presaturating current'efiect, the maximum impedance of the desaturated reactor would be passed and the impedance thereafter decreased so that the phase shift would then start to change i in the opposite direction. In order to accomplish this control, .I provide a. reference voltage which is proportional to the maximum impedance condition of the desaturated reactor which may be a component of voltage proportional to the presaturatingcurrent or bias magnetomotive force and combine this component of voltage with a component of voltage proportional to the control current of the saturable reactors. In the circuit illustrated the reference component of voltage for one direction of armature current is derived from a resistor IOI connected in series relation with the output circuit of the rectifier 131) which is a. substantially constant voltage output derived from the circuit of the presaturating windings Il2. For the reverse direction of armature current the reference component of voltage is derived from a resistor IOIa. connected in series with resistor IOI. It will, of course, be understood that any other constant reference voltage may be used without departing from my invention in its broader aspects if such component of voltage bears the above described relation to the maximum impedance condition to the desaturated reactor. The variable component of voltage proportional to the control winding current may be obtained from the armature current of the mechine I9 and as illustrated is derived from the resistor 90 in the armature circuit of machine I9.

The left-hand terminal of field winding 84 is connected to one terminal of resistor I0 Ia through a contact rectifier I02 which is poled in a direction to pass current in the direction of the arrow when the variable component of voltage from resistor 90 isgreater than the reference voltage. The current limit circuit may now be traced from positive terminal of resistor 00, through the resistor I 0Ia, through rectifier I02 to the left-hand terminal of field winding 84, through field winding 84 to the negative terminal of resistor 90. The rectifier I02 renders the circuit unidirectional so that there is no current traversing the current limit field 84 until the component of voltage from resistor 90 exceeds the reference component of voltage from resistor I0-Ia. However, with the assumed polarities it will be noted that when the armature current of machine I9 raises the positive potential of resistor 90 abovethat of the reference potential, field winding 84 is energized from left to right which makes the positive brush 82 less positive and therefore limits the arma ture current.

When the current in the armature of the controlgenerator I9 is in the reverse direction, the voltage component across resistor 90 is in the reverse direction from that assumed above and it is then necessary to select a reference voltage which is also reversed from that previously assumed in order to have the two components opposed. Hence, the resistor IN is connected in series with the componentof voltage across resistor 90 through a contact rectifier I 02a. In

this case, the current limit circuit may be traced from the left-hand terminal ofresistor (now 'group of conductors I I5 to a suitable rectifier I I4 plus), through field winding 84, through rectifier I02a, through resistor IOI back to the righthand terminal of resistor 90 (now negative). The rectifier I02a renders this circuit unidirectional so that there is no current traversing the current limit field 84 until the component of voltage from resistor 90 exceeds the reference component of voltage from resistor IOI. It will be observed that the right-hand terminal of field winding 84, is indicated as positive for the first conditions assumed'but under the last assumed reversal of armature polarity of the machine I9 its righthand brush 82 is now positive and hence a positive potential on the right-hand'terminal of field winding 84 tends to make the brush less positive and thereby limit or reduce the armature current in the reversed direction.

Since consideration of the load transfer field 8! involves a number of devices at the opposite end of the system and illustrated in Fig. 2, such consideration will be deferred until later and the excitation and control of the load control field 86 will now be considered. In principle, when the tube groups 3 and 4 are operated as rectifiers the machine I9, through the phase shift circuit 26, operates as a regulator balancing the load current of the conversion apparatus against 9. reference voltage or signal. A measure of the load current of the converter is secured by rectifying the output of current transformers connected in the input circuit i to the rectifier. Thus on the previously stated assumption the apparatus of Fig. 1 will be considered as the 60 .cycle rectifier end and that of Fig. 2 as the output or 25 cycle inverter end, a component of voltage proportional to the load current is derived from current transformers I03 associated with circuit I. The output of current transformers I03 is converted through transformer I 04 to an A.-C. voltage component and this, voltage component is transferred through a group of conductors I05 to'a suitable rectifier I06. A resistor I0I is connected across the rectifier I06 and is provided with an adjustable tap I08 to provide a convenient adjustable voltage component corresponding to the load current of theconverter. This component of voltage may thus be referred to as the load voltage EL. This component of voltage corresponding to rectifier load current is arranged to oppose a reference component of voltage which may be referred to as ER. The reference voltage Ea may be obtained from a suitable adjustable source of constant voltage which remains substantially constant at the adjusted level. In practice, I have found that a three-phase induction regulator I09 having its shunt and series windings connected in a manner to provide a threephase voltage of adjustable magnitude makes a satisfactory reference voltage. The induction regulator as illustrated is connected to be energized from the bus 21A. The output circuit of the device I09 is connected to a transformer II 0 which is provided with a primary winding III and in order to provide a reference voltage for both ends of the system, two secondary windings H2 and H3, respectively, are also provided. The output voltage of the secondary winding II! is connected to a suitable rectifier II4 for use at the 60 cycle end of the system (Fig. 1) and the secondary winding H3 is connected through a for use at the 25 cycle end of the system (Fig. 2). A pair of resistors I I6 and III are connected in series across the output of the rectifier H4 and are provided with adjustable taps H8 and H9,

respectively,to make available the adjustable reference component of voltage En. The adjustable contacts I" of the Ex. resistor and IIS of the ER resistor are connected together and provided with Y a connection terminal I20 which is connected through an Is'witch I2I to the left-hand terminal of field winding 86. The lower terminal of resistor I01 is connected through an R switch I22 to the left-hand terminal of, winding 86. The adjustable contact H3 01' the Ea resistor is connected through an R switch I23 to the righthand terminal of winding 86. The energization of winding 88 during rectifier operation of the tube groups 3 and 4 will now be evident. It will be noted that the reference voltage component Ea and the load current voltage component Ex. are connected in series opposition across the field winding 88. With the R switches I22 and I23 closed the circuit may be traced from contact ill, the positive terminal of the reference voltage En, through R switch I23,

through winding 86 from right to left, through R switch I22, through load current resistor IIII, back to the negative terminal H9 of the reference voltage resistor I II. The difference between the reference voltage Ea and the load voltage Er. will act on the control field 86. If the load is lower than is desired, the reference voltageEa will exceed the load voltage E1. and will excite the field winding 86 from right to left in a, direction to change the saturating current of control saturating windings I3 to 18 in a direction to Just the initial advance of the inverter grids. A suitable rectifier I23 is connected to the bus 21a and a resistor I23 is connected thereacross and provides a convenient source of D. C. voltage corresponding to the output voltage of the inverter tube groups 3 and 4 when these tubes are operating as inverters. This component of voltage may be used in an additive direction, as illustrated, to the reference voltage Ea. Still another component of voltage is derived from the bus 21a through a negative phase sequence network device I3Il, the output of which is rectified by a suitable rectifier I3I having a resistor I32 connected thereacross. The component of voltage from resistor I32 is in the same direction as the reference voltage Ea and is utilized to modify the control in the event of phase unbalance in the inverter output circuit. The lower terminal of resistor I32 is connected to the contact III on'the reference voltage resistor through an I switch I33. The energizing circuit for winding 36 during inverter operation will now be evident. Starting with the left-hand terminal of winding 36, the circuit may be traced through I switch If], reference resistors II3-I I1, I, switch I33, negative phase sequence resistor I32, in-

verter bias resistor I28, armature current'resis- 'tor 33 and to the right-hand terminal of wind- 1 ing 36. With this circuit Just traced, if the refadvance the rectifier grids and thereby increase the load to the value set by the reference voltage En. 0n the other hand, if the load be greater than is required as determined by the reference voltage Ea, the reverse action will take place and the rectifier grids will be retarded.

The induction regulator I" may be operated in rwponse to several methods of regulating the load such as manual control, watt control or demand watt control. The various novel features involved in these several controls for regulator I39 are described and claimed in an application of Gittings and Bateman, Serial No. 560,161, filed October 24, 1944, now Patent No. 2,407,072 of September 3, 1946, and assigned to" the assignee of the present application. For purposes of simplicity, I have shown a manual control which includes, as a suitable driving means for the rotatableelement of the device I09, a reversible motor I 24 connected through a suitable shaft and gearing I25 to the rotatable element of the induction regulator. As a, means for controlling the direction and amount of rotation of the motor I23 I have shown a reversing switch I28 connected between the motor I24 and a source of voltage I21 indicated by the and signs.

The field winding 38 is controlled in accordance with the same reference voltage Ea when the tube groups 3 and I are operated as inverters, although other variable components of voltage are related to ER. vThe same reference voltwinding 86. One of the three components is a.

voltage component Ep derived from the resistor 83 or a portion thereof as illustrated which is proportional to the armature current of the machine Another component which may be referred to as inverter bias is derived from the voltage of the bus I through the bus 21a, to aderence voltage is higher than the resultant of the other three components'of voltage,v more load is being indicated and the winding 38 will be energized in'a direction from right toleft under the assumed polarities and make the lefthand brush 32 more positive. to cause the phase shift circuit to advance the inverter grids. In this way the inverter grids are advanced to maintain an approximately constant margin angle or deionization angle the importance of which was explained above. I

The final feature of field control to becon- I sidered is that involving 'the energization of winding 35 which is herein referred to as load transfer control. However, since winding- II is dependent for its energization upon the apparatus shown in Fig. 2, a brief description of that figure now will aid in a consideration of the load transfer control. Since the various elements and devices at the two ends of the system are substantially identical, except for design changes that may be necessitated by two different frequencies, all the elements and devices of Fig. 2, which has been assumed to be at the 25 cycle end, have been given the same reference numerals, with a prime mark, as the corresponding elements and devices'of' Fig. l. The only exception to this system of identification is that part of the main power circuit which has been previously described.

The mechanism and system of load transfer involving the energization' of field winding 25 of generator I 9 may now be considered when thepreviously considered tube groups 3 and 4' and thus the 60 cycle end is being operated as 'an inverter with power fiow from circuit 2 to circuit I. The

ponent of voltage sothat field winding 35 of generator I! (now at the inverter end) is energized when the component of voltage corresponding to the armature current of the control generator at the rectifier end exceeds the reference voltage. The reference voltage may conveniently be obtained from the resistor IOI'a. which is connected in circuit with the output of the presaturating current rectifier ll'p. A component of voltage, which is variable in accordance with the armature current of the control generator I9 is obtained from the resistor 90' which is connected in series with the load brushes 22'. These two componentsof voltage are connected in a circuit with opposed polarities through a conductor I94 which interconnects the positive terminal of the reference-voltage resistor IOIa and the positive terminal of the armature-current resistor 90. A conductor I95 is connected to the negative polarity tap IOI'b on resistor IOI'a through an adjustable resistor I56, 9. contact rectifier I 31', one side of the circuit maybe traced to the right-hand terminal of winding 85 of machine 19 (Fig. 1) by way of conductor I25. A conductor I59 is connected to the ne ative terminal of resistor and may be traced to the left-hand terminal of winding 85 (Fig. 1) Hence, these two components of voltage from resistor 90' and resistor IOIa ,are connected in series opposition and transferred from Fig. 2 to winding 85 on Fig. 1 by conductors I35 and I39. These components of voltage are so re-' assumed rectifier control generator I0. exceeds a predetermined value, the positive component of voltage from armature current resistor 90' is enabled to send current in the conducting direction of rectifier I31 so as to send a current through winding 95 from right to left and cause the control generator I9 to advance the phase of the network 26 which advances the inverter grids and thereby transfers load control to the inverter end of the system.

Load transfer is effected from the control gen- A. H. Mittag, filed October 1, 1941, now Patent No. 2,362,294. of November '7, 1944, and assigned to the assignee of this application. This type of ignitor circuit is very diagrammatically indicated in Fig. 1 and comprises, as part of its principal components, a firing capacitor I42 and a firing reactor I43 which is designed to saturate during each half wave of alternating voltage of the circuit I40 by reason of the discharge of current from the firing capacitor I42 through the primary winding I45 of transformer I4. The firing circuit may also include a linear reactor I46 connected between the circuit I40 and the firing capacitor I42 to prevent discharge of the capacitance to the supply circuit I40 and also to limit the current taken from the supply circuit at the time the capacitance discharges through winding I45. The transformer I44 may be an insulating transformer, as illustrated, which is provided with a pair of secondary windings I41 and I48 and is utilized to transform the ignitor peaks up to the high voltage level of the tubes. Hence,

one terminal of the secondary winding I41 is connected to the ignitor electrode 23 of the upper righthand tube in tube group 4 through a contact rectifier I49, and the other terminal is connected to the cathode'22 of this same tube. The ignitorof the opposed tube of this tube pair would be connected to winding I48 in a similar manner. It is to be understood that the firing peaks of firing reactor I43 occur on both the positive and negative half cycles of the source voltage and thus the single firing reactor I43 provides two peaks displaced 180 degrees apart so erator 19 of Fig. 1 when it is operating as a rectito determine the instant of conduction in each tube both an ignitor energizing circuit I40 and a grid energizing circuit I are arranged for each pair of tubes which are to be conductive 180 degrees apart. For the .purpose of simplifying the drawing, only one of each of the respective excitation circuits is shown in diagrammatic detail, although it is to be understood that ignitor and grid excitation circuits similar 'to those illustrated will be connected, as will be understood by those skilledin the art, to 'the'respective pairs 01' valves and to the-proper points onv the phase shift network 20 and 20' with due regard to the phase of the anode voltages of the particular pair of tubes 1 to be .controlled. A suitable arc initiating circuit for tubes of the ignitor type, as illustrated, may be ofthe socalled magnetic impulse type such as is described and claimed in an application 8. N. 413,232 of as .to serve for firing, two opposed tubes.

A suitable grid firing circuit is described and claimed in my application Serial No. 539,941, filed June 12, 1944, now Patent No. 2,419,465 of April 22, 1947, andassigned to the assignee of thepresent application. Hence, in the system illustrated I have shown the grid excitation circuit quite diagrammatically but in suflicient detail to incorporate the essential features thereof. I again illustrate an insulating transformer I50 comprising a primary winding I5I which is connected to the grid supply circuit MI and a pair of secondary windings I52 and I53. One terminal of the secondary winding I52 is connected to the cathode of the upper right-hand tube of tube group 4. The secondary winding I52 supplies a potential to the holding anode circuit 24 through a transformer I54 and to the grid25 preferably through a peaking transformer I55. A suitable bias means, indicated by the battery I56, is connected in the grid circuit to hold the tube off or specifically to hold the grid negative until the positive peaker voltage overcomes the bias and renders the tube conducting. The secondary winding I53 would be connected to the grid and holding anode circuits of the oppositely disposed tube of the two tube groups of tube group 4 in a manner understood by those skilled in the art.

In connecting the ignitor circuit I40 and the grid circuit Hi to the phase shifter 26, it is necessary to determine the phase of the anode voltage of the particular pair of tubes under consideration and the relation between the several voltages of the respective electrodes of the tube. For the pair of tubes of tube group 4 illustrated, with the ignitor and grid circuits illustrated in diagrammatic detail, it will be assumed that the anode voltage has the phase position indicated by the arrow marked anode in the center of phase shift circuit 28. If the firing circuit voltage forthe ignitor goes through zero at a given angle displaced from zero anode voltage, which we may assume for purposes of illustration is'of the order of 140 degrees advance for the three-phase full wave connection illustrated, the firing reactor would cause the ignitor to fire at a point of the order of 30 degrees after the zero phase of anode voltage. Hence, the ignitor firing circuit I40 would be connected to taps on :phase shifter 26 such that a linethrough the taps will be substantially parallel to a line advanced of the order of 140 degrees relative to the phase of the anode voltage shown. In the drawings, the tap connections indicated for the assumptions made are taps 50a and 59a.

If the grid peaker IE is arranged to fire at the 65 point of the voltage impressed thereon, this means that the grid voltage goes through zero some 35 ahead of the zero phase of the anode voltage and the grid circuit I is connected to taps 56a and 58a on the polygon windings 31 to 48 such that a linetherethrough is advanced substantially 35 ahead of the assumed phase of the anode voltage. The arrangement and connection of the ignitor circuit I40 and the grid circuits I4I' of the tube groups 5 and 8 are made to phase shift network 26' in a similar manner to that described in connection with phase shift network 26.

The general operation of the illustrated embodiment of my invention may now be considered briefly. It was considered expedient to describe briefly the operation of the various component parts and elements in connection with the initial consideration of these elements so that the general overall operation may be more easily understood.

In the illustrated embodiment of the invention above described the system rectifies altemating current from the supply end, such as circuit I, by the tube groups 3 and 4 to direct current which traverses the .direct loop comprising con-' ductors 3a to 4b to the inverter tube groups 5 and 6 where conversion is effected to alternating current which is supplied to circuit 2. The direction of power fiow is determined by the phase angle of grid excitation. Thus, if it is desired to transmit power from circuit I to circuit 2, all It switches associated with the apparatus of circuit I will be closed while all I switches at this rectifier end will be opened; Conversely, all 'I switches associated with the apparatus of circuit 2 at the inverter end will be'olosed while all R switches will be opened. With the amplidyne generators 19 and lil operating, the induction regulator I09 will be adjusted to set the reference voltage Ea at such a value as to effect substantial equality between the rectifier voltage and the inverter counter voltage, so that no power is interchanged over the D.-C. loop. For this condition the amplidyne generator I9 will supply current to the phase shifter control windings I3 to I8 so that the rectifier grids are fully retarded as explained above and themverter grids of the tube groups 5 and i are ad'- vanced by phase shifter 26' the minimum desired amount for a proper commutation angle as determined by the inverter bias resistor 13'. Power transfer from circuit I to circuit 2 is then increased by adjusting the induction regulator I09 at some predetermined setting corresponding to the desired load. The amplidyne generator I9 through the action of the control fieldwinding 86 will then decrease the energization of the phase shift control windings I3 to I8 from full excitation in one direction which provides the 90'degree phase retard through zero to full excitation in the opposite direction for full grid advance or such excitation as will provide the necessary phase shift. corresponding to the load setting previously set by regulator I09. If it be assumed that the load setting required full phase advance of the rectifier grids and the desired load was not yet attained, the load transfer mechanism would immediately function in response to a predetermined armature current of the amplidyne generator I9. If this armature current limit is exceeded, the voltage component derived from resistor 90. which is proportional to the armature current of amplidyne I9, would cause energization of field winding of the amplidyne I! at the inverter end and cause the voltage of this amplidyne to change in such a direction as to change the saturation of control windings 73' to I8 of phase shifter 20' to change in such a direction as to effeet a greater phase advance of the grids of the inverter tube groups 5 and 6. The advance of phase of the inverter tube groups reduces the counter E. M. F. of these tube groups and thus transfers load control to the inverter end. As a result, it has been found that increasing the inverter load angle, while holding the rectifier grids fixed, results in a larger load with an approximately constant margin angle. A similar sequence of operations would be effected if power transfer were in the reverse direction, namely from circuit 2 to circuit I.

Now while the tube groups 3 and 4 were as sumed to be operating as rectifiers, I also previously stated that the tube groups 5 and 6 were assumed to be operating as inverters with the I switches closed and the R switches open. Under inverter operation, the ignitor andgrid circuits of these tubes are initially adjusted for the proper advanced phase shift for inverter operation. The phase adjuster 26', with the I switches closed. has a phase range of the order of 60 degrees. Aside from the feature of load transfer control effected through winding 85' the inverter ,tubes through the phase shifter 26' are responsive to four components of voltage, namely the reference voltage E'a from adjustable contacts lit-I III, a component of voltage dependent upon inverter unbalance and, hence, derived from the negative phase sequence network I30, a component of voltage dependent upon the voltage of the circuit 2 derived from inverter bias resistor I29 and a component of voltage dependent upon the armature current of the amplidyne generator 19' derived from resistor One important feature of the control on the inverter grids is the relation between the amplidyne armature current and the reference voltage. When the reference voltage E'a, which is also the reference voltage of the rectifier end, calls for a larger load,- the control winding 86' is energized with a different current which acts through the phase shift control windings I3 to 18' to advance the inverter grids. In this way, the inverter grids are advanced to maintain an approximately constant marginangle or deionization angle. The two additional components of voltage provide correction for the inverter bias and phase unbalance in the inverter, if necessary, through modification of the excitation of winding 86' and hence result in a phase shift of the inverter grids to effect the desired correction. The tube groups 3 and 4, when operating as an inverter, operate in substantially the same manner as has been described for tube groups 5 and 6. Load transfer control from the tube groups 5 and 6 operating as rectiflers to tube 15 groups 3 and 4 operating as inverters is 'efiected through armature current resistor 90' and the load transfer circuit comprising conductors 535' to I39 to the load transfer field winding 85 of ampiidyne generator 19. I

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a dynamo-electric machine having an armature winding, a first control field winding, 8. second control field winding, means for energizing said first control field winding in a direction to effect an increase in the armature current above a predetermined value, means for producing a reference component of voltage, means for producing a component of voltage proportional to current in said armature winding, and means including a unidirectional conducting device for connecting said components of voltage in opposed relation responsive tothe current of said armaturewinding for energizing said second control field winding only when said armature current exceeds said predetermined value and in a direction to limit the current of said armature winding to said predetermined value.

2. In combination, a dynamo-electric machine having an armature winding, a first control field winding, a second control field winding connected upon energization to oppose the magnetization of said first control field winding, means for energizingnsaid first control field winding in a direction to effect an increase in the armature current above a predetermined value, means for producing a component of voltage of constant value, means for deriving a component of voltage variable in accordance with the armature winding current, means for connecting said components of voltage in opposed series relation to energize said second control field winding, and a unidirectional conducting device conected in series relation with said second control winding and being poled to conduct current only when said variable component of voltage exceeds said component of voltage of constant value.

3. In combination, a dynamo-electric machine having an armature winding, a first control field winding, a second control field winding, means for energizing said first control field winding -in a direction to eflect an increase in the armature current above a predetermined value, means in- 16 eluding a resistor connected in series relation with said armature winding for deriving a component of voltage variable in accordance with said armature current, means for deriving a constant component of voltage, means for connecting said components of voltage in opposed relation to energize said second control field winding, and unidirectional conducting means connected in series relation with said second control field winding for selectively causing energization thereof to limit saidarmature current when said first men-. tioned component of voltage exceeds said constant 1 component of voltage. v

4. In combination, a reversible polarity ampiidyne generator having. an armature winding, a control field winding for said armature winding, a second field winding for said armature winding and being provided with end terminals, means for energizing said control field winding in a direction to effect an increasein the armature current above a predetermined value, means including a first resistor connected in series relation with said armature winding for deriving a component of voltage variable in accordance with said armature current, means including a pair of series connected resistors having an intermediate junction terminal and a pair of end terminals, means for energizing said pair of resistors for providing equal and constant components of voltage across the respective resistors oi. said last mentioned series connected resistors, a closed circuit including a'pair of opposed unidirectional conducting devices having a Junction terminal said armature current for either polarity 01 volt- I ageof said generator when-the component of voltage across said first resistor exceeds the constant component of voltage across either one of said series connected resistors.

. BURNICE D. BEDFORD.

REFERENCES The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,134,880 McDowell et a1 Nov. 1, 1938 

